A self-test apparatus for examining the sight of the two eyes of a patient, and for self-screening for visual defects without intervention of an operator is especially known from document EP0102887_B1. The apparatus includes an optical system that allows test images borne by a roll of film to be viewed, said test images being presented along three distinct optical channels, corresponding to near-vision, far-vision and intermediate-vision distances, respectively. Advantageously, the self-test apparatus includes a loudspeaker circuit and a recording circuit that are coupled and/or synchronized with the rotation of the roll of film, in order to give instructions and/or ask questions to the patient and to record the responses of the patient depending on the viewed test images.
An apparatus for screening for visual defects is also known, under the trade name Ergovision by Essilor, which allows optical tests or optotypes to be presented at various vision distances. The person tested passes from far vision, to intermediate vision then to near vision simply by lowering his gaze. A voice-synthesizing device allows the sequence of a series of tests to be automatically controlled. The patient may respond to the questions via buttons of a remote control.
The test images or optotypes used in these screening apparatuses, for example to measure visual acuity or to screen for hypermetropia, are in general alphanumeric characters arranged analogously to a Monoyer scale of eye tests. These tests allow clear instructions to be given such as, for example: “read line No. X”, and allow easily understandable responses to be recorded.
Nevertheless, alphanumeric-type test images are not usable with illiterate people. Furthermore, visual acuity measurement bias may arise from memorization of series of letters or numbers by the patient or from a tendency of the patient to guess more than view the displayed alphanumeric characters.
However, the screening of visual defects must now conform with the standard ISO8596, which not only defines the optotype presentation distances but also the form of the optotypes.
According to this standard, the optotypes must be presented at a distance corresponding to a far vision larger than 4 meters. The near-vision distance is not standardized but a distance range comprised between 33 and 50 cm is commonly cited.
In addition, according to the standard ISO8596, visual screening tests must be based on a Landolt scale, which includes a series of identical optotypes, which are called Landolt rings, taking the form of circles comprising an aperture or break. The diameter of the circle varies depending on the tested visual acuity. The orientation of the aperture of the circle varies in various directions that may be: 0, +45 degrees, +90 degrees, +135 degrees, +180 degrees, +225 degrees, +270 degrees and +315 degrees relative to a vertical line.
The Landolt scale has the advantage of being able to be used by illiterate people. In addition, it is difficult for a patient to guess a lighter or darker zone corresponding to the orientation of the aperture of a Landolt ring. In theory, the Landolt scale allows acuity measurements not bringing into play the memorization of the morphology of a letter. In practice, for a given acuity to be tested, i.e. for a Landolt ring of determined diameter, the ring is presented with a random orientation a certain number of times so as to make it possible to determine whether the visual performance is achieved or not.
However, the oral response of a patient to indicate the orientation of a Landolt ring raises problems of reliability. Specifically, though the indications top and bottom are widely assimilated by all of the population, the notion of right and left may be subject to confusion. For the other directions, such as +45 degrees, +135 degrees, +225 degrees and +315 degrees, it is in general very difficult to be sure of the relevance of the response. This use of a Landolt scale may lead to an incorrect response from the user, even though this user has visually detected the correct orientation of the ring.
It is therefore necessary to be able to record the responses of the patient to a test based on a Landolt scale in a trustworthy way that does not introduce false positives.
Some known apparatuses presenting Landolt rings use a joystick by way of user interface. If the use of such an accessory is familiar to a population accustomed to videogames, it is not completely spontaneous for a novice.
In general, the visual screening apparatuses of the prior art do not allow the Landolt-scale test images indicated in standard ISO8596 to be used reliably.
One of the aims of the invention is to provide an apparatus and method for screening for defects in the sight of a person allowing, in a compact volume, optotypes, in particular taking the form of Landolt rings, to be presented at two very different vision distances and a reliable response of the tested person to be recorded.